1. Field
The present invention relates generally to telecommunications, and, more specifically, the invention relates to multiple-input multiple-output (MIMO) cellular communication systems.
2. Background
A modern communication system is expected to provide reliable data transmission for a variety of applications, such as voice and data applications. In a point-to-multipoint communications context, known communication systems are based on frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and perhaps other multiple access communication schemes.
A CDMA system may be designed to support one or more CDMA standards, such as (1) the “TIA/EIA-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (this standard with its enhanced revisions A and B may be referred to as the “IS-95 standard”), (2) the “TIA/EIA-98-C Recommended Minimum Standard for Dual-Mode Wideband Spread Spectrum Cellular Mobile Station” (the “IS-98 standard”), (3) the standard sponsored by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents known as the “W-CDMA standard,” (4) the standard sponsored by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including the “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” and the “TIA/EIA/IS-856 cdma2000 High Rate Packet Data Air Interface Specification” (the “cdma2000 standard” collectively), (5) the 1xEV-DO standard (occasionally referred to as simply “DO”) with its revisions 0/A/B, and (6) certain other standards. The standards expressly listed above are incorporated by reference as if fully set forth herein, including annexes, appendices, and other attachments.
Data-optimized or “DO” cellular communication systems have been developed to satisfy the constantly increasing demand for wireless data services. Data-optimized systems include systems operating under the 1xEV-DO standard mentioned above. As the name implies, DO systems are optimized for data transmission (as opposed to voice transmission), and in particular such systems are optimized for downlink data transmission. Data-optimized systems need not exclude uplink data transmission, or voice transmission in either direction. It should be noted that voice may also be transmitted as data, for example, in the case of voice over internet protocol (VoIP) transmissions.
A MIMO system employs multiple (NT) transmit antennae and multiple (NR) receive antennae for data transmission. A MIMO channel formed by the NT transmit and NR receive antennae may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensions created by the multiple transmit and receive antennae are used.
For a full-rank MIMO channel, where NS=NT≦NR, an independent data stream may be transmitted from each of the NT transmit antennae. The transmitted data streams may experience different channel conditions (e.g., different fading and multipath effects) and may achieve different signal-to-interference-and-noise ratios (SINRs) for a given amount of transmit power. Moreover, if successive interference cancellation processing is used at the receiver to recover the transmitted data streams, then different SINRs may be achieved for the data streams depending on the specific order in which the data streams are recovered. Consequently, different data rates may be supported by different data streams, depending on their achieved SINRs. Since the channel conditions typically vary with time, the data rate supported by each data stream also varies with time.
The use of MIMO transmission techniques allows increased spectral efficiency, an important performance characteristic of wireless systems.
Therefore, there is a need in the art for methods, apparatus, and articles of manufacture that would allow the use of MIMO techniques in wireless systems, including cellular wireless systems. There is also a need in the art for methods, apparatus, and articles of manufacture that would allow the use of MIMO techniques while maintaining backward compatibility with legacy access terminals. There is a further need for methods, apparatus, and articles of manufacture for adapting existing data-optimized systems such as systems operating under the 1xEV-DO revisions 0, A, and B for operation employing MIMO techniques.